This invention relates to a component for producing semiconductor devices and a process for producing the component, and especially to a component such as a process tube or a boat for containing and supporting wafers in a diffusion or CVD (Chemical Vapor Deposition) process.
In the past, components for producing semiconductor devices were mainly made of a silicon carbide (SiC) material.
Components made of silicon carbide for producing semiconductor devices have excellent strength but also have a lot of impurities in comparison with components made of quartz or silica glass (more than ten times as many).
Components made of such a silicon carbide material have high porosity and a poor sealing characteristic so that, when semiconductors are produced, the impurities contained inside the components contaminate the semiconductor devices. Among the impurities, alkali or the like can be effectively removed by a HF-HNO.sub.3 treatment, but it is very difficult to remove heavy metals such as Fe. As is well-known, such impurities contaminate semiconductor devices when they are produced. In particular, a component, such as a boat semiconductor wafers directly contact is liable to contaminate devices by diffusion of impurities to a large extent.
In order to solve such defects, various improvements have been made. For example, as disclosed in Japanese Patent Publication No. 60-45154, there is proposed a refractory material having a composite-material layer formed on a heat-resistance body such as a silicon carbide body by a chemical vapor deposition method. For example, such a composite-material layer is formed of plural deposit-layers which are combinations of a silicon carbide layer and a silicon nitride layer.
Japanese Patent Laid-Open No. 62-122212 also proposes a component for semiconductor devices having a silica (SiO.sub.2) layer of a thickness of 20 to 100,000 .ANG. on a surface of a high purity Si-SiC body.
However, in conventional methods proposed to solve the above defects, the requirement of avoiding contamination and providing a high strength protection layer are not met. Especially, the component described in Japanese Patent Laid-Open No. 62-122212 doesn't have a strong surface because the surface is made of a silica layer. Also, the silica layer is liable to peel off because of its large thickness.